Coater hardware and method for obtaining uniform photoconductive layers on a xerographic photoreceptor

ABSTRACT

A method and device for obtaining uniform vapor deposition of one or more inorganic metallic photoconductive materials onto a substrate by importing under vacuum a slow translational movement of one or more heated crucibles and/or of the substrate being coated.

This invention relates to a device and method for obtaining a moreuniform vapor deposition of inorganic metallic coating material such asphotoconductive material onto a suitably prepared receiving surface suchas a substrate by varying the position of the vapor source with respectto the receiving surface.

BACKGROUND

It is customary in the xerographic art to form an electrostatic latentimage on a photoreceptor drum or plate comprising a charge conductivebacking such as, for example, a metallic or metal coating surface havinga photoconductive insulating layer applied thereto in good chargeblocking contact. A suitable device for this purpose comprises, forexample, an aluminum plate having a thin layer of vitreous selenium andan aluminum oxide and/or polymeric interlayer. Such a plate ischaracterized by being capable of excepting a suitable electrostaticcharge and of quickly and selectively dissipating a substantial part ofthe charge where light is exposed. In general, such photoreceptors aresensitive to light in the blue-green spectral range.

While selenium containing photoconductive elements are usefully employedin commercial xerography, there is room for substantial improvement inphotoconductive properties such as the range of spectral response, heatand charge stability, etc. These can be improved by the addition ofvarious photoconductive alloys, alloying elements or other types ofadditives (ref. U.S. Pat. Nos. 2,803,542 and 2,822,300). For example,the addition of various amounts of arsenic can result in a broader rangeof spectral sensitivity and improve overall photographic speed andstability. Suitable alloys or homogeneous mixtures of elemental seleniumwith other metals suitable for this purpose can also be incorporatedinto the usual photoconductive material by conventional vacuumevaporation techniques. For example, additional inorganic coatingmaterials can be placed in open or shuttered crucibles in a vacuumduring an initial coating step. The xerographic substrate upon which thephotoconductive material is to be deposited is conveniently placed aboveor in some other convenient location with respect to the potentialcoating vapor source. After the container has been evacuated to asuitable pressure (about 5 × 10⁻ ⁵ Torr), the vessel containingphotoconductive material and/or additive is then heated by suitablemeans known to the art such as by electric resistance heating elementsto promote vaporization of the material. At least some of the vaporizedmaterial then condenses on the relatively cool substrates; such adeposition process normally requires a period of about 15-60 minutes,depending upon the amount of substrate surface to be coated and thedesired thickness of coating material.

From time to time it is also found desirable to apply profileconcentrations of one or more photoconductive components or separatelayers of different photoconductive materials to obtain a particulardesired spectrum of characteristics. In such case, the respectivephotoconductive materials or alloys are most conveniently applied tosubstrates or bases by coevaporation techniques, in which predeterminedamounts of the respective photoconductive materials or alloys are placedin separate crucibles or in subdivided crucibles and exposed or heatedin a predetermined sequence under vacuum. One very useful modificationfor this purpose involves coating in the presence one or a plurality ofelongated crucibles heated by electrical heating elements or by otherconventional means, the crucibles being subdivided into a plurality ofcompartments or bins, each capable or carrying different amounts andkinds of coating materials depending upon the desired finalconcentration. Another useful modification involves the formation of oneor more trains of small crucibles temporarily connected to each otherand containing various photoconductive materials. Both arrangements arefound to be very useful in coating a plurality of substratessimultaneously with a plurality of components.

Unfortunately, however, the use of such crucibles separated by bafflesor end walls also presents serious technical problems insofar as it isdifficult to control surface irregularities and achieve consistencyduring batch coating. This is found to be due largely to variation inthe geometric relation of substrates to crucible bins and particularlyattributable to the presence of crucible end walls or baffles. Suchcoating irregularities, in turn, usually cause unacceptable variationsin electronic properties both between and within the individualphotoreceptors being batch produced.

It is an object of the present invention to develop a method andequipment for efficiently and evenly batch coating one or more receivingsurfaces or prepared substrates with one or more coating materials orcomponents thereof.

It is also an object of the present invention to minimize or avoidirregularities when batch coating one or more inorganic photoconductivematerials onto prepared xerographic substrates in a vacuum coater.

A still further object relates to obtaining an improved method forimprovement quality of batch coated xerographic photoreceptorscontaining one or more photoconductive components.

THE INVENTION

The above and other objects are achieved in accordance with the presentinvention wherein receiving surface, inclusive of xerographic substratesor bases, are batch coated with at least one vaporizable coatingmaterial or component thereof and applied under vacuum from one or moreevaporation crucibles containing a plurality of subdivisions delimitedby baffles or end plates and crucible walls, and arranged in convenientproximity to the receiving surfaces.

The process as envisioned requires the steps of heating one or morematerial-containing crucibles simultaneously or in sequence while movingat least one of said (a) crucibles or said (b) receiving surfaces in atranslational manner along parallel planes with respect to each other.

A particularly suitable batch coating device within the scope of thisinvention for achieving the above objects and described process (i.e.vacuum coating vaporizable coating materials or components thereof ontoreceiving surfaces) comprises, in combination,

a. one or more evaporation crucibles arranged within a vacuum coater inconvenient proximity to receiving surfaces to be coated, said cruciblesbeing elongated and having a plurality of subdivisions delimited bybaffles or end plates and crucible side walls;

b. mounting means for movably holding receiving surfaces in the sameparallel planes within the vacuum coater in convenient proximity to thecrucibles and coating material;

c. supporting means for movably supporting one or more crucibles in thesame or parallel planes within the vacuum coater at points below themounted receiving surfaces;

d. heating means arranged for separately or concurrently vaporizingcoating material from all or subdivisions of each crucible as desired;and

e. means for moving one or both of said crucibles and said receivingsurfaces within the vacuum coater in a translational manner duringcoating.

The device, as described, is best utilized for coating coating materialor components thereof onto mounted receiving surfaces by heating one ormore of the crucibles under vacuum and moving at least one of said (1)crucibles and said (2) receiving surfaces in translational movementalong parallel planes with respect to each other.

DESCRIPTION OF DRAWINGS

The concept as envisioned is further described with respect to essentialcomponents of a suitable batch coating device although not limitedthereby. FIG. 1 is an isometric fragmentary view, FIGS. 2--5 areorthographic cross-sectional views and FIG. 6 is a three-dimensional orperspective view of representative components of the present invention.

In particular, FIG. 1 is illustrative of a suitable embodiment of thepresent invention wherein base member (15) and rails (13) as well as arotatable or rotating reciprocating spindle 8 are affixed orconveniently mounted within a vacuum coater capable of achieving anatmospheric pressure to about 5 × 10⁻ ⁵ Torr in general accordance withknown coating procedures. Such general procedure and vacuum coatingtechniques are described, for instance, in U.S. PAT. Nos. 2,753,278,2,970,906, 3,311,548 and 3,490,903.Removable elongated evaporationcrucibles exemplified by 9 are subdivided by baffles or end plates 12for holding individual coating compositions or components thereof 10 andequipped with resistance heating elements 11 plus sliding means 14adapted for a back and forth translational movement along a plane withinthe coater. Actuation means (not shown) permit movement of crucible 9back and forth along rails 13 during coating and, if desired, areciprocating as well as a rotational movement of spindle 8.

One or more receiving surfaces demonstrated as drums of suitablestructural integrity, here shown in the form of mountable drums, 7 aremounted on a metal spindle 8 in convenient proximity to crucible 9. Asnoted above, the mounted receiving surface or drum can optionally alsomove in a translational manner as well as rotate about the axiscorresponding to spindle 8.

FIGS. 2-5 relate to various modifications of self-heating cruciblesshowing parts corresponding to FIG. 1 including crucibles 9B-9E, slidingmeans 14A-14D, coating materials 10A-10D and electrical heating elements11B-11E. The later elements can be usefully eliminated, if desired,provided the crucible itself comprises a material having sufficientresistivity to act as the heating element.

FIG. 6 exemplifies a further modification within the scope of thepresent invention in which a crucible 9A containing resistance heatingmeans 11A is mounted on a base 20 containing 21-24 for imparting arotational translating movement of said crucible in convenient proximityto receiving surfaces shown as a plurality of drums 7A removably mountedon a rotatable spindle 8A having the dual ability to axially rotate and,if desired, to move back and forth in an axial translational direction,the long axis of the crucible being generally parallel with the drumaxis or spindle 8A.

Generally speaking, a receiving surface for purposes of the presentinvention is inclusive of surfaces of plates, flexible belts, drums,sheets, webs or miscellaneous-shaped objects, the only limitation beingthat the object being coated be sufficiently stable when exposed toheats of vaporization and condensation of the coating material utilized,and that the coating material adequately adhere in stable condition tothe surface being coated. In this connection, it is noted thatxerographic substrates or base plates such as stainless steel, aluminum,copper, brass, nickel, chromium, metal coated glass or the like havingsuitable oxide or other intermediate blocking layers and also charge orhole transport layers, if desired, are well suited for covering in theabove manner.

The coating materials 10-10E of FIGS. 1-6 represent one or more separatecoating materials or components of coating materials of metallic ornon-metallic types, the principle criterion being that the materialbeing applied have a sufficiently high vapor pressure under heat and avacuum (up to about 5 × 10⁻ ⁵ Torr in the case of a photoconductivematerial) to evaporate and condense onto the desired receiving surfacewithin a reasonable time and without undesired chemical changes to thecoating material or the receiving surfaces.

Photoconductive materials being applied in the present manner arepreferably although not exclusively inorganic photoconductive materialsor additives thereof. Suitable materials for coating within the presentinvention can also include vaporizable monomeric materials for, in situ,polymerization onto a substrate as well as amorphous selenium, variousselenium alloys with arsenic and/or tellurium, etc., and optionalhalogens or sensitizing dyes such as disclosed in U.S. Pat. No.3,532,496. Such materials can be conveniently placed in adjacentsubdivisions of each crucible in sequence below each drum, belt, orplate, etc., to be coated or some even applied in separate adjacentcrucibles of a stationary or nonstationary type.

The spindle 8, 8A, end plates 12, 12A, rails 13, and comparable orequivalent means FIG. 6, No. 21-24 are preferably although notexclusively of stainless steel.

For purposes of the present invention it is also useful to includeevaporation crucibles of steel, ceramic or comparable materials oreither conventional open boat or of a tube type. Such include, forinstance, modified crucibles which avoid the risk of spattering ofcoating material such as described in U.S. Pat. Nos. 3,748,090 and3,746,502.

It has also been found that the method and device above exemplified anddescribed is best carried out when one or more crucibles are moved inlong axial direction with respect to a plurality of stationary receivingsurfaces, particularly xerographic substrates or bases although thereceiving surfaces, or both crucibles and receiving surfaces, can bemoved out of sync to assure adequate coverage. In any case, the movementwith respect to the crucibles and receiving surfaces is that of arelative translational motion during deposition. For this purpose, oneor more crucibles (or receiving surfaces) can be slowly moved withrespect to a plurality of receiving surfaces (or crucibles) as abovedescribed, the movement of each crucible (or receiving surface) beingabout 1/4 to about 2 times the long axial distance of a cruciblesubdivision, preferably being unidirectionally displaced about 1 inch to6 inches and completing each cycle of movement in about 5 - 60 secondsand particularly 5 - 10 seconds.

A further advantageous arrangement involves arranging the receivingsurfaces in the form of drums axially rotatably mounted convenient to atleast one crucible, the long axis of each drum being arranged paralleland above the long axis of each crucible.

What is claimed is:
 1. A method for batch coating xerographic substratesor bases with at least one vaporizable photoconductive coating materialor component thereof applied under vacuum from one or more evaporationcrucibles containing a plurality of subdivisions delimited by baffles orend plates and crucible walls and arranged in convenient proximity tothe xerographic substrates or bases being coated, comprising heating andvaporizing photoconductive material from one or more cruciblessimultaneously or in sequence while moving at least one of said (a)crucibles or said (b) xerographic substrates or bases in a translationalmanner along parallel planes with respect to each other.
 2. The methodof claim 1 wherein the heated crucibles, individually contain at leastone photoconductive material, the crucibles being moved in long axialdirection with respect to a plurality of stationary xerographicsubstrates or bases.
 3. The method of claim 1 wherein the crucibles arestationary and individually contain at least one photoconductivematerial.
 4. The method of claim 1 wherein the heated cruciblesindividually contain at least one photoconductive material and both thephotoconductive materials and xerographic substrates are subject to arelative translational motion during deposition.
 5. The method of claim2 wherein one or more crucibles are slowly moved with respect to aplurality of xerographic substrates or bases, the movement of eachcrucible being about 1/4 to about 2 times the long axial distance of acrucible subdivision.
 6. The method of claim 3 wherein each xerographicsubstrate is slowly moved about 1/4 to about 2 times the distance of astationary crucible subdivision.
 7. The method of claim 4 wherein thexerographic substrate and the photoconductive material are movedrelative to each other bout 1/4 to about 2 times the distance of acrucible subdivision.
 8. The method of claim 5 wherein one or morecrucibles move unidirectionally about 1 inch to 6 inches and a completecycle of movement is effected in about 5-60 seconds.
 9. The method ofclaim 6 wherein the substrates or bases move unidirectionally about 1inch to 6 inches, and a complete cycle of movement is effected in about5-60 seconds.
 10. The method of claim 7 wherein the crucibles and thesubstrates or bases move undirectionally about 1 inch to 6 inches, and acomplete cycle of movement is effected in about 5-60 seconds.
 11. Themethod of claim 8 wherein a complete cycle of movement is effected inabout 5-10 seconds.
 12. The method of claim 1 wherein the receivingsurfaces are in the form of drums axially rotatably mounted convenientto at least one crucible, the long axis of each drum being arrangedparallel and above the long axis of each crucible.
 13. The method ofclaim 2 wherein the xerographic substrates are charge conductive drums,belts, matts or plates.
 14. The method of claim 2 wherein thexerographic substrates are charge conductive drums, belts, matts orplates.
 15. The method of claim 3 wherein the xerographic substrates arecharge conductive drums belts, matts or plates.